Precipitation refers to any form of moisture that falls from the atmosphere to the earth's surface. It includes rain, snow, sleet, and hail. Therefore, out of the options given, the correct answer is "dust." Dust is not a form of precipitation, but it can be suspended in the air and transported by wind currents. Dew and fog are not considered precipitation either, as they are formed through the condensation of moisture in the air rather than through the falling of moisture from the atmosphere.